This invention relates to coronary angioplasty and, more particularly, to an absorbable stent for placement within a blood vessel, such as a coronary artery, at the locus of a stenotic lesion.
A technique for coronary angioplasty has been developed which generally involves the use of a catheter system including a dilation catheter which is introduced via the femoral artery, under local anesthesia, and advanced to the site of a stenotic lesion in a coronary artery. An extensible balloon mounted on the distal end of the dilation catheter is inflated with a fluid once it is disposed within the target stenotic portion of the coronary artery. As the balloon is inflated, the atherosclerotic material in the vessel is compressed in a direction generally perpendicular to the wall of the vessel which, consequently, dilates the vessel to facilitate blood flow therethrough. While this technique has been rather successful in a number of instances, restenosis is common and, in the event the plaque cracks during expansion, subsequent collapse of the coronary artery is likely. It would therefore be desirable to minimize restenosis of the vessel by maintaining the plaque in its compressed disposition while, at the same time, preventing collapse of the vessel subsequent to plaque dilation. One manner in which the foregoing can be achieved is by placing a stent within the afflicted vessel at the locus of the stenotic lesion after the plaque has been dilated or, preferably, at the time of plaque dilation.
One such stent has been proposed and tested in Europe and described in the article of Stignart, et al. titled "Intravascular Stents to Prevent Occlusion and Restenosis after Transluminal Angioplasty", published in the New England Journal of Medicine, Vol. 316, No. 12, Mar. 19, 1981, pages 701-706. This stent is in the form of a "Chinese finger handcuff" metallic mesh which can be expanded and compressed in diameter. The stent is made by cutting desired lengths from an elongated tube of metal mesh and, accordingly, has the disadvantage that metal prongs from the length cutting process remain at the longitudinal ends thereof. The inherent rigidity of the metal used to form the stent together with these terminal prongs make navigation of the blood vessels to the locus of the lesion difficult as well as risky from the standpoint of injury to healthy tissue along the passage to the target vessel. Further, when this stent is permanently placed in a coronary artery, the continuous stress from the beating of the heart would cause the prongs to damage the healthy vessel walls adjacent to the lesion. This damage could lead to arterial rupture or aneurysm formation. Finally, because it is adapted to be chronically implanted within the vessel, the continued exposure of the stent to blood can lead to thrombus formation within the blood vessel with dilitarious results.
It would therefore be desirable to provide a stent that has sufficient structural integrity to be placed within a vessel at the site of a stenotic lesion to support the vessel wall against collapse and yet is flexible and compliant enough for safe and effective delivery to the site of a coronary obstruction. It would further be desirable to provide a stent which is soft and compliant enough to avoid arterial rupture or aneurysm formation at the ends of the stent even when exposed to continuous stresses from the beating heart during chronic implantation. It would also be desirable to provide a stent which avoids the limitations of chronic implantation by becoming absorbed into the vessel wall after healing of the angioplasty site. It would be further desirable to use a bioabsorbable material that could be formed in such a way, i.e., in a mesh-like or porous configuration, that will enable endothelial cells at the angioplasty site to grow into and over the stent so that bio-degradation will occur within the vessel wall rather than in the lumen which could lead to embolization of the dissolved material.